Prevention of apoptosis in CNTF-dependent neurons by a mutant ICE and by viral protein CrmA but not by proto-oncogene product Bcl-2.

The interleukin-1beta converting enzyme (ICE) gene family, (homologues of C. elegans cell death gene product Ced-3) plays an important role in controlling programmed cell death. Nerve growth factor (NGF) promotes survival of cultured embryonic chicken dorsal root ganglion neurons. Ciliary ganglion neurons depend exclusively on ciliary neurotrophic factor (CNTF) for survival. Complete depletion of NGF or CNTF from culture medium induces apoptosis in both types of neurons. We can prevent apoptosis, due either to NGF or CNTF withdrawal and in either type of neuron, by overexpression of a mutant inactive ICE and an ICE inhibitor, the product of cowpox virus gene crmA. Bcl-2 does not prevent apoptosis in CNTF-dependent ciliary neurons or DRG neurons as it does in NGF-dependent neurons. These results suggest that neuronal cell death is mediated through a common effector mechanism involving the Ice family of genes, whereas different suppression mechanisms are engaged depending upon the specific neurotrophic factors present.